In general, data generated by applications or users for some purposes is stored in various data storage systems according to the data types, purposes of later use of data, and management purposes. For example, the following data storage systems are widely used today:    File system in which data is stored in units of files and data is stored in a tree format called a “directory tree”.    Relational database in which tables, each composed of multiple-column records, are created by defining and formatting data according to given meaning or purposes.
A file system is widely used as a storage destination of data created by applications or users, because in general there is no limit on the size of data that can be stored in a practical range and because data may be stored in a data structure called a “file” that has not a special data structure.
Data stored in a file system is managed using a tree format, called a “directory tree”, in which file names are used as nodes. This means that, when extracting data, the user cannot access data, unless the user does not specify the location of data, that is, a pathname on the directory tree, in order to access data, based on the file name mapped on the directory tree.
The file system manages not only data itself but also the following data as metadata.    File name    File size    Time data such as data update time    Data on a person, such as a data owner, responsible for data processing
However, data is extracted basically by specifying a pathname only.
For this reason, when data is processed by an application via a file system, the user can extract data quickly by recognizing the pathnames of necessary files. However, when the user wants to extract data based on information on non-pathname data, the extraction processing takes long even if the information is metadata managed in the file system.
As described above, a file system, though higher in the flexibility of data that can be stored, is inferior in the ability to search for data.
A relational database is a storage system for use in a data usage environment where contents of data can be structured. In a relational database, data is represented in the form of records, classified and arranged in advance according to predetermined items, and multiple records are managed as a two-dimensional table for fast data search.
In a relational database, all items used for classifying and arranging data may be used as an information extraction key and, so, only the required information can be extracted very quickly. For this reason, a relational database, a storage system best suited for storing and using structured data, is widely used as a storage system especially for an application that performs routine work.
However, a relational database, which limits the size of data that may be stored in a record, is ineffective means for storing non-structured data.
As a result, a relational database, though superior to a file system in the ability to search for data, is lower in the flexibility of data that can be stored.
Today, the best storage system for the requirements to be satisfied by a particular system is selected, and data is stored in various data storage methods, as described above.
In a data sharing environment in which data, stored in those storage systems, is used by multiple other systems, each application must work with the data creation source system to convert the data format used by the data creation source to the data format used by the data usage location.
To solve this problem, Patent Document 1 discloses a system in which data stored in multiple storage systems, which have different data types and different data access means, is mapped to a single data representation so that the data can be processed as objects. And, by newly providing a single data access interface via which data is accessed on an object basis, the system hides data access means, specific to each storage system, from applications to allow data to be shared among applications which use different data formats and run in different storage systems.
Patent Document 2 discloses UIMA (Unstructured Information Management Architecture) used to develop applications that integrate the search and analysis of a combination of structured information (DB) and unstructured information (documents). UIMS (Unstructured Information Management System) includes search engines, data storage areas, analysis engines including pipelined document annotators, and various adapters. A search inquiry includes search operators (Boolean predicate that functions as weighted AND) composed of multiple search partial expressions each of which has an associated weight value. The search engine returns one or more documents having a weight value sum that exceeds the threshold weight value sum.
Patent Document 1:
Japanese Patent Kokai Publication No. JP-A-H11-327997
Patent Document 2:
Japanese Patent Kokai Publication No. JP2004-362563A